The mechanical properties of metal oxide coated polyester films

This communication reports on a study of the microstructure, mechanical and gas barrier properties of PECVD metal oxide coatings on heat stabilised (HS) PET [poly(ethylene terephthalate)], primer-coated HS PET, filled PET and PEN [poly(ethylene naphthalate)] substrates. The coatings are highly conformal and exhibit very few large scale defects. Internal stresses in the coatings are found to be compressive for all substrates. The substrate is found to influence some of the mechanical properties with the cohesive strength of the coating greatest for primer-coated HS PET and lowest on filled PET. Secondly, a primer layer also increases the adhesive strength between coating and substrate compared to plain PET and PEN. Substrate surface roughness is found to influence the morphology of the SiO x films but does not seem to adversely affect the barrier performance of the composites. We found that heat stabilised PET, with or without an additional acrylate primer layer and PEN produce superior composites than untreated PET film in terms of water vapour barrier. Using a mass spectrometry detection technique we measured a WVTR value as low as 2 × 10 -4 g m -2 day -1 for 1 μm thick coatings on PEN.